Abstract Magnetic anisotropy of the
MnxFe3-xO4 (x = 0.99, 1.24, 1.6) single
crystals was measured down to liquid helium temperatures using the torque
method. Fourier analysis of the torque curves in the (100), (110) and (111)
crystallographic planes showed that in these ferrites the anisotropic part of
the free energy cannot be properly described by means of the first and the
second cubic anisotropy constants only. The explanation of this anomalous
behaviour is given taking into account that there is a strong coupling between
the electrons of the Mn3+ ion and the crystal lattice (strong
Jahn-Teller-effect).